Vibratory devices are used in many applications to perform a wide variety of functions. A vibratory finishing machine, for example, generally includes a movable tub or bowl mounted on a fixed base. Piece parts to be finished are loaded into the tub or bowl together with a suitable finishing media, which typically comprises a mixture of abrasive material and liquid, such as water, and an optional finishing agent. As the tub is vibrated with an eccentric actuator mounted thereon, relative movement between the piece parts and finishing media causes performance of the desired deburring, burnishing, polishing or other finishing operation on the parts.
The eccentric actuators typically employed with such machines include either a rotatable shaft with eccentric weights mounted thereon, or simply a rotatable eccentric shaft. In either case the shaft of the eccentric actuator can be supported by antifriction bearings of the ball, roller, tapered roller or needle type; however, several problems have arisen in the use of bearings with rolling and nonrolling elements in such applications. The useful lives of such bearings are relatively short because repeated radial loads cause fatigue and localized heat buildup leading to early bearing failure. Replacement of the bearings supporting eccentric actuators has been a continual and persistent problem in the use of vibratory machines.
More recently, hydrodynamic bearings have been developed for supporting the eccentric actuator of a vibratory machine. Such bearings utilize a thin film of fluid between certain moving parts to reduce the fatigue and heating problems otherwise accompanying direct mechanical contact between the parts. Circulation of the fluid has been especially effective in controlling heat buildup in such bearings, however, sudden bearing failure can occur if the proper hydrodynamic film is not maintained. Maintenance of sufficient fluid film thus has been of critical importance to the operation of hydrodynamic bearings.
U.S. Pat. No. 3,954,309 assigned to the assignee hereof, discloses a vibratory actuator which incorporates the principle of deflection matching between the shaft and the housing within which the hydrodynamic bearings are supported to faciliate maintenance of sufficient fluid film by minimizing structural deflection and misalignment. This device, although effective, is axially supported at opposite outboard ends and some difficulties from excessive end thrust have been experienced. In addition, this approach requires precise engineering analysis and construction to match the stiffnesses of the shaft and housing, and requires precise machining to make coaxial bearings concentric and in line, which in turn results in extra weight and cost.
A need thus exists for an improved vibratory actuator which by simple means assures deflection matching between the shaft and housing while facilitating maintenance of the proper fluid film in the hydrodynamic bearings, which permits greater latitude for errors in concentricity and alignment of coaxial bearings, and which further provides axial support for the shaft to accommodate end thrust loads without excessive heat and wear.